Learning Forum

[Ian2860]

Hello all! Beginner user here.

I have a lot of meshing problems and I don't know where to begin solving them. Here are my errors/warnings when I did the mesh check:

• Warning: non-positive volume exist
• Warning: #faces have warp greater than or equal to 0.5
• Warning: buildings: 5 left-handed faces
• Warning: interior-p-468: 75 left-handed faces

My skewness is also so bad. I am not so sure where to start with all these errors.

I want to do a coarse mesh first because I just want to know if the geometry works.

I use Fluent 2020 R2, btw, and I attached pic of my geometry.

[Keyur Kanade]

The min orthogonal quality should be above 0.1 to proceed to solver. If it is less than 0.1 then please improve the mesh.
First check the locations of the bad elements. Please see following video for the same.

https://www.youtube.com/watch?v=ZDADSSN8hOs

Once you have locations, please check if you can improve mesh using different mesh sizing. Please see following video.

https://www.youtube.com/watch?v=w4q6q8nKF3U

If this does not help, you may need to check if you can use pinch control or virtual topology.

https://www.youtube.com/watch?v=wdKMqfJV1Ys
https://www.youtube.com/watch?v=RELLrEJ9chg

If this does not help, please go to geometry and modify or simplify geometry at those locations in SpaceClaim.
Regards Keyur
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[Ian2860]

Thank you very much! I will try all your suggestions :)

[Rob]

I'd also check to see if those chimneys are cylinders or hollow tubes. If they're the latter I'd be considering changing them to the former.

[Ian2860]

Hello sir. They are not hollow but not a cylinder either. They are more like pipes? This is the picture of the cross-section of one chimney. Inlet located at the base.

[Rob]

In a build environment model I'd use a cylinder and add material at the top: you can't afford the cell count to resolve inside the stack like that.

[Ian2860]

Thank you for your suggestion sir. I have modified my chimney to the picture attached. I just want to clarify what you mean by adding material at the top? Does this mean inlet assignment?

[Rob]

Yes, if you're adding smoke/pollutants. Otherwise they're just cylinders. CFD is a powerful tool but needs care in it's application: this includes working out what to include in the model. Look over the remainder of the model for similar issues, you may have other small features that are causing you problems with the mesh.